Organic Analysis Flashcards
How to test for primary, secondary or tertiary alcohol?
1) Add 10 drops of the alcohol to 2 cm3 of acidified potassium dichromate solution into a test tube
2) Warm the mixture gently in a hot water bath
3)If primary = orange solution will slowly turn green as the aldehyde forms
Secondary = orange solution slowly turns green as a ketone forms
Tertiary = no change
To then find if it is primary or secondary
1) Add the excess alcohol to 2 cm3 of acidified potassium dichromate solution in a round bottomed flask
2) Set up the flask as part of distillation apparatus p162
3) Gently heat the flask, the alcohol will be oxidised and the product will be distilled off immediately so you can test it
How to test is you have an aldehyde or a ketone?
Fehling’s solution and Benedict’s solution
1) Add 2cm3 of either solution to a test tube (will be blue)
2) Add 5 drops of the aldehyde or ketone to the test tube
3) Put the test tube in hot water bath for a few minutes
Aldehyde - blue will give a brick red ppt
Ketone - no change
Tollens reagent
1) Put 2cm3 of 0.10 mol dm-3 silver nitrate solution to a test tube
2) Add a few drops of dilute sodium hydroxide solution. A light brown ppt should form
3) Add drops of dilute ammonia solution until the brown ppt completely dissolves
4) Place the test tube in a hot water bath and add 10 drops of aldehyde or ketone and wait for a few minutes
Aldehyde = silver mirror forms on the walls of the test tube
Ketone = nothing happens
How to test for alkenes?
1) Add 2cm3 of the solution that you want to test to a test tube
2) Add 2cm3 of bromine water to the test tube
3) Shake the test tube
Alkene = the solution will decolourise - orange to colourless
Not alkene = nothing happens
How to test for carboxylic acids?
1) Add 2cm3 of the solution that you want to test to a test tube
2) Add 1 small spatula of solid sodium carbonate
3) If the solution begins to fizz, bubble the gas through some limewater in a separate test tube
Carboxylic acid = the solution will fizz, the carbon dioxide gas that is produced will turn the limewater cloudy
How can mass spectrometry help to identify compounds?
For any compound, the m/z value of the molecular ion peak will be the same as the molecular mass of the compound
see example on another card
Example
The mass spectrum of a straight chain alkane contained molecular ion peak with m/z = 72.0.
Identify the compound
1) the m/z value of the molecular ion peak is 72.0 - so the Mr of the compound is also 72.0
2) If you calculate the molecular masses of the first few straight chain alkanes you’ll find the one will molecular mass of 72.0
3) so the compound must be PENTANE
High ________ mass spectrometers can measure atomic and molecular masses extremely accurately
resolution
If needed to work these out you will be given precise atomic masses to work out the answer (decimal places)
_______ spectroscopy helps you to identify organic molecules
How?
infrared
The IR radiation is absorbed by the covalent bonds in the molecules, increasing the vibrational energy.
Bonds between different atoms absorb different frequencies of IR radiation - given in a table
The ________ region identifies a molecule
Fingerprint
The region between 500cm-1 and 1500cm-1 is the fingerprint region. It is unique to a particular compound.
How does infrared radiation absorption link to global warming?
Some of the electromagnetic radiation emitted by the sun reached the earth and is absorbed. The earth then reemits some of this as infrared radiation
Molecules of greenhouse gases like CO2 in the atmosphere absorb this infrared radiation. They then reemit some of this back toward earth keeping us warm. This is called the greenhouse effect.
Human activities such as burning fossil fuels and leaving rubbish to rot in landfill have caused a rise in greenhouse gases
This means that more heat is being trapped and the earth is getting warmer - this is global warming.
